Impedance Mismatch(?) Help

CDLehner

CDLehner

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So...last night; I experienced something, I have never encountered...or not nearly to such a degree.

As some of you know...I'm a box-hoarder, or really more of an audiophile "bulimic" (pardon, but it's true). I buy, buy, buy...stuff that catches my eye; until my listening room, overrunneth with kit...and then it's time to pick and "purge".

So I'm putting pre-amps to power-amps last night (we'll withhold the names of the innocent, for the time being)...and I'm getting, like no output! I reboot my Aurender, I power-down the DAC; make sure their link is good. I check, re-check...all cables and fittings; go from single-ended to balanced...ins and outs.

Then, I notice...if I go all the way up to like 12 o'clock; I get the faintest whisper of my music. I know it almost sounds as if something was set-up "wrong", and I was getting bleed-through; but it eluded me...and I know my way, around the back of gear. So I don't think so. EVERYTHING the same, swap another pre-amp in...and we're off and running.

Could my impedance mismatch, between pre-amp and amp...have been this bad? Let me know the numbers I need to get you, and I'll do my best (they are not, current models).

Thanks :S
 
Chris-How do you know that the preamp you swapped in that you couldn't hear hadn't shat the bed since the last time you used it? Since you are not telling us what preamp into what amp, it's premature to declare no volume to be caused by an impedance mismatch.
 
I am guessing you may have hit a wrong input or something similar. I am guessing you are hearing a faint bleed through between inputs.

Another option is you mixed inputs and outputs.
 
mep said:
Chris-How do you know that the preamp you swapped in that you couldn't hear hadn't shat the bed since the last time you used it? Since you are not telling us what preamp into what amp, it's premature to declare no volume to be caused by an impedance mismatch.
Click to expand...

It had only been, like 2 weeks since I used it last; successfully...with another amp.
 
still-one said:
I am guessing you may have hit a wrong input or something similar. I am guessing you are hearing a faint bleed through between inputs.

Another option is you mixed inputs and outputs.
Click to expand...

Jim...it was late; I'll grant you that. But I'll swear I checked, re-checked, and triple-checked...pretty damn carefully.

But of course...I'll be trying again tonight; and the acid test is...if I get the same result, hooking it up to the amplifier it worked fine with before.
 
There is no way an impedance mismatch between a preamp or power amp should cause zero output from the amp. The highs might be rolled or the bass may be funky sounding, but you should have amplification. Just don't drink 14 beers before you lash it up and you should get sound unless the preamp is broken. :D
 
Chris, I bet you just had something either cabled incorrectly or an input/output selection that was wrong.
 
That's starting to seem like the consensus :blush:

Now I'm beginning to wish, I hadn't posted, lol. I'll re-hash it all tonight.
 
CDLehner said:
That's starting to seem like the consensus :blush:

Now I'm beginning to wish, I hadn't posted, lol. I'll re-hash it all tonight.
Click to expand...

Hey, we all screw up sometimes-trust me. And yeah, it's embarrassing when a friend of yours comes over and politely points out that you have your head up your ass on something, but we all do it at one point or another. It usually happens when we are swapping out gear. It's also possible that your preamp broke since the last time you used it. Remember, everything works until it breaks. How many times have you gone to use something and it was broken and the first words out of your mouth are "But it was just working"?
 
mep said:
Hey, we all screw up sometimes-trust me. And yeah, it's embarrassing when a friend of yours comes over and politely points out that you have your head up your ass on something, but we all do it at one point or another. It usually happens when we are swapping out gear. It's also possible that your preamp broke since the last time you used it. Remember, everything works until it breaks. How many times have you gone to use something and it was broken and the first words out of your mouth are "But it was just working"?
Click to expand...

So true, so very true
 
OK...ate some dinner, gathered my senses (and flashlight); and started from the beginning.

I still say the impedance match, is not "optimal"...as I've got to lay really heavy, on the pre's volume, to get the levels I like; but it's not as it was last night.

But common as it is to do...I still won't cop, to flipping a cable. You can't connect XLRs incorrectly! :P
 
CDLehner said:
OK...ate some dinner, gathered my senses (and flashlight); and started from the beginning.

I still say the impedance match, is not "optimal"...as I've got to lay really heavy, on the pre's volume, to get the levels I like; but it's not as it was last night.

But common as it is to do...I still won't cop, to flipping a cable. You can't connect XLRs incorrectly! :P
Click to expand...


No, sort of-more about that in a minute. What you can do is what Gary and others said, and that is hooking up your source to your preamp to an input that you didn't intend and selecting the input you thought you had it on and only hearing a faint whisper from your amp.

As for not being able to connect an XLR incorrectly, it's possible with enough force and stupidity. I have seen not so good techs plug in a mil keyed connector incorrectly with enough force that they broke off the key and jammed the connector into the female input connector and damaged all the pins and ruined both connectors.
 
mep said:
What you can do is what Gary and others said, and that is hooking up your source to your preamp to an input that you didn't intend and selecting the input you thought you had it on and only hearing a faint whisper from your amp.
Click to expand...

Well...I guess there's no way to say for certain, I didn't; and I will say...this pre, does have assignable inputs and outputs.

But man...I must have been just locked-in on stupid, for about an hour! :huh:

I'd still love, for someone who understands those output of pre-amp, and input of amp; to take a look at the appropriate numbers, and tell me this isn't a great match...ability-to-dynamically-drive wise.
 
Power amp input impedance should be at least 10x the output impedance of a preamplifier and higher than 10x is generally better.
 
MikeCh said:
Power amp input impedance should be at least 10x the output impedance of a preamplifier and higher than 10x is generally better.
Click to expand...

OK...here are the pre-amp output numbers



...and the amp's input numbers



See a potential for "issues"; because it wasn't a very good pairing, IMO.
 
As far as driving voltages there is no problem with those specs being a mismatch, but you need to consider the ratio of the preamp's output impedance (not provided above) to the amp's input impedance as MikeCh specified. So as long as the preamp's output impedance is less than or equal to 10K ohms single ended and 20K ohms balanced it should be fine.
 
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